MEMS micro-actuator, also known as an executing unit or actuating unit, is a device which can transfer energy into a controllable movement and a power output according to a control signal. Micro-actuator is an important MEMS device, and is widely applied to the fields such as optics, communication, biomedical science, and micro-fluidics. The micro-actuator mainly includes a transducer which transfers an electric energy into a mechanical energy, and a micro-structure which performs a power output. According to an energy source, actuators can be divided into an electrical actuator, a magnetic actuator, a thermal actuator, an optic actuator, a mechanical actuator, an acoustic actuator, a chemical actuator and a biological actuator, the common driving modes include an electrostatic mode, an electromagnetic mode, an electro-thermal mode, a piezoelectric mode, a memory alloy mode, an electrostriction mode, and a magnetostriction mode.
The electrostatic actuator takes advantages of an electrostatic attraction between the energized conductors to realize a drive. An efficient of the electrostatic drive is relative higher when in a small size (1 to 10 micrometers), and it is easy to be implemented and accurately controlled, and special materials are not required, it is the most widely used driving mode. The electrostatic actuator includes a plate capacitor structure, a comb fork structure, a rotatable electrostatic motor, and a linear long distance actuator, which takes advantage of electrostatic forces along a perpendicular direction and a parallel direction.
The plate capacitor actuator is a commonly used electrostatic actuator, the lower electrode plate of the capacitor is fixed, and the upper electrode plate can move when it is supported by an elastic structure. When a driving voltage is applied to the upper electrode plate and the lower electrode plate, the electrostatic attraction between the plates drives the whole upper electrode plate to move perpendicularly, and an output is realized. The manufacture of the plate capacitor actuator is simple, and it is can be easily controlled and used, but a driving distance is little, and an output force is little. The output driving force and the capacitor has non-linear relationship, and a push down is easy to emerge when it is controlled by a voltage, an effective driving distance is limited. In addition, when in a dynamic condition, the damping of the pressed film of the plate capacitor is relative larger, limiting the dynamic range.
The torsional electrostatic actuator takes advantage of a torsional cantilever beam and an electrostatic force to torque the upper electrode plate to realize an output, the torsional electrostatic actuator has a better performance, this is because the torsion movement can output a relative larger driving force than a perpendicular movement. The conventional torsional electrostatic actuator has a relative small output force due to the limitation of the manufacture technology.